The present invention relates generally to the field of devices for propelling particulate matter with intent to etch the surface of a target material. More specifically, the present invention relates to a micro abrasive blasting device with a sealed reservoir powered by a pressurized-gas source for use with dental procedures.
There are many devices and methods for impacting the surface of a target material with particulate matter. Devices of many sizes and types are available for this process, and many types of pressurized gases such as air, nitrogen, oxygen, and others power them. These devices operate on the physical property that gas at higher pressure flows towards and into gas at lower pressure. When particulate matter is mixed with gas at higher pressure, the gas carries the particulate matter as the gas accelerates and flows to the lower pressure. As the gas and particulate matter blast the target material at high speed, the impact of the particles removes layers of the target material.
This process of material removal is commonly known as etching and also as sandblasting. As the rate of the target material removal increases, the etching process can be utilized for drilling and cutting. More specifically, the aggressiveness of the particulate impact-speed and frequency determine the rate of material removal, and thus whether an abrasive blasting device is useful for polishing, etching, or drilling. Particulate impact-speed and frequency are adjusted by variation of the gas flow rate and gas-to-particulate mixture ratio.
The aggressiveness of the etching process is also a function of the particulate matter. Specific to dentistry, hard aluminum oxide particles are normally utilized for etching and cutting, while softer particles such as sodium bicarbonate are used for cleaning and polishing. Other types of particulate materials with various harnesses are used to achieve various operational objectives.
In dentistry this technology is known as micro-abrasion and is used to achieve a variety of goalsxe2x80x94such as to remove foreign material or to dull a shiny surface, roughen or etch the surface to enhance bonding quality, and to remove decay by drilling and cutting tooth structure. Micro-abrasive blasting devices for dental applications strive to utilize particulate materials with small particle diameters. Smaller particles provide finer micro-pores and less discomfort to the patient. More refined particulate materials also wash quicker and easier from the mouth, again adding to patient comfort level. The major problem with using finer particulate matter is their higher sensitivity to moisture. Moisture in fine particulate matter causes the particles to clump together thus changing their flow properties.
Some etching devices compensate for variation in flow properties by adding mechanisms that remove moisture or clear clumped particles in order to facilitate consistent mixing action. Other devices use mechanical agitation and complex plumbing to facilitate mixing of the gas and abrasive particles. These devices also use various forms of flow control.
One device that provides adjustable flow control is the Paasche device, U.S. Pat. No. 2,441,441. The Paasche device is still widely used by dentists. The device utilizes a screw mounted into the reservoir closure cap to regulate the amount of abrasive contained in the air stream. The screw is manually adjusted to regulate the gas-abrasive mixture by providing means for varying the gap between the screw tip and gas-abrasive exit tube.
The mixing method utilized by Stark et al., U.S. Pat. No. 4,475,370, Hertz, U.S. Pat. No. 5,839,946, and Schur et al. U.S. Pat. No. 6,004,191, provides a simple device with no moving parts and a single mixing chamber.
The mixing chamber has only one port for pressurized gas delivery and only one discharge port for gas-particulate mixture release.
The Stark et al. device was designed to operate in the dental lab for material preparation. Stark et al. makes the device refillable by providing a closure cap carrying a gas-delivery conduit for replenishing the device with abrasive material for repeated use. Hertz and Schur et al. disclose the use of a pre-filled and sealed particulate-mixing chamber. The Hertz and Schur et al. design hinder particulate contamination in order to create a device suitable for intra-oral use, by forming a single-use device that can not be readily refilled once the particulate matter is depleted.
The invention disclosed herein solves multiple significant shortcomings with the Stark et al., Hertz, and Schur et al. devices that use this mixing method.
(a) Their first shortcoming is due to the physical properties of the abrasive material in the reservoir.
(I) The gas-delivery conduit carried by the closure cap of the Stark et al. device is difficult to push into the reservoir during cap closure. It is especially difficult when the reservoir contains hard abrasive particles. The resistance of the particulate matter against the gas-delivery conduit during the closure of the reservoir cap causes the gas-delivery conduit to deform as it is inserted. Deformation such as bending may cause the gas-delivery conduit to change the direction of the delivered gas, thus changing the mixing pattern and reducing the effectiveness of the device operation.
(II) It is also likely that during the insertion of the gas-delivery conduit, abrasive particles would get jammed in the gas-delivery conduit, thus causing a restriction in the conduit delivering gas into the device. Both Hertz and Schur et al. experience this same difficulty as they insert the gas-delivery conduit into the mixing chamber during the assembly process of their devices. Since their devices are pre-filled and sealed, testing for this assembly failure can not be performed. This means that the user discovers this defect at time of use.
(b) A second shortcoming is that when the particulate matter is poured into the Stark et al. device some abrasive material enters the discharge conduit and exits the device. This restricts the locations where the device can be refilled, since the abrasive particles are very damaging to mechanical equipment, work surfaces, and are not very pleasant to the touch. Again, both Hertz and Schur et al. experience this same difficulty as they fill their devices with measured amounts of particulate matter during the assembly process.
(c) A third shortcoming solved by the present invention is due to the sensitivity of the abrasive particles to moisture in the atmosphere. Moisture in the air causes the abrasive particles to stick together thus reducing the mixing efficiency of the device. This leads to the potential clogging of the discharge conduit during operation. Therefore, if the Stark et al. device is not used immediately after the reservoir is replenished with dry particulate matter, there is the potential for degradation in performance or failure of the device to operate due to moisture.
Hertz recognizes the moisture and contamination issue. Hertz discloses an inlet cap for sealing the gas-receiving port and a tip cap for sealing the distal end of the particle-directing tube external to the chamber. Since Hertz""s tip cap resides on the distal end of the particle-directing tube external to the chamber, during the abrasive filling operation or movement of the device prior to use, abrasive material travels into the discharge conduit. This trapped abrasive material can not be removed from the discharge conduit prior to use by turning the device over, since the abrasive material internal to the chamber blocks the discharge conduit inlet.
Some of this trapped abrasive material spills out of the discharge conduit when the tip cap is removed from the Hertz device. However, some of the abrasive material trapped in the discharge conduit compacts and clumps inside the discharge conduit. In some instances this trapped material may obstruct the discharge conduit and prevent the device operation. In other instances the clumped material is released when pressurized-gas is first applied to the device. Since the abrasive particles in the discharge conduit do not go through the mixing chamber, the initial pressurized-gas application causes the trapped abrasive to be released in a dense clump. This abrasive clump release causes an initial puff of abrasive that is inconsistent with the normal pace of particulate delivery during the device operation. This initial blast of abrasive may also damage the target surface by over etching.
(d) A fourth shortcoming is the risk of utilizing a tip cap for sealing the distal end of the particle-directing tube external to the chamber. Failure of the user to manually remove the Hertz tip cap prior to application of pressurized-gas, could result in the tip cap becoming a dangerous projectile as the gas-particulate stream propels it. The tip cap is especially a liability when the Hertz and Schur et al. devices are used on patients.
(e) A fifth shortcoming is the use of removable inlet and tip caps by Hertz.
(I) The need to remove the caps prior to use significantly inconveniences the userxe2x80x94dentist or dental assistantxe2x80x94which profits by rapidly completing a procedure.
(II) The caps are a liability, since during the removal of the caps in preparation for use, there is the potential of misplacing a cap. Since the patient may be already in the dental chair with the mouth open, any loose components must be carefully accounted for.
(f) A sixth and major drawback of these devices is that no mechanism for regulating the gas-abrasive mixture is provided. The implication of this drawback is that multitudes of devices must by configured to achieve various operational ranges of gas-abrasive mixtures and flow rates. Such configurations provide devices with gas-abrasive flows that are individually optimized for specific use. Physical device configurations range from light gas-abrasive flow for light etching to aggressive gas-abrasive flow that is sufficient for drilling and cutting.
Accordingly, several objects and advantages of the present invention are:
(a) to provide a device with more consistent operation by eliminating the potential for deformation of the gas-delivery conduit during cap closure.
(b) to provide a more reliable device by eliminating the potential for clogging of the gas-delivery conduit during gas-delivery conduit insertion.
(c) to provide a device that is not messy to fill by eliminating spillage of abrasive through the discharge conduit.
(d) to provide a device with better operational performance by eliminating the potential for abrasive material to accumulate in the discharge conduit.
(e) to provide a more reliable device by eliminating the potential for abrasive material to obstruct the discharge conduit.
(f) to provide a device that is safer to use by eliminating the potential for the tip cap to dislodge off the particle-directing tube when pressurized-gas is applied.
(g) to provide a device that is safer and more convenient to use by eliminating the need for the user to remove caps prior to operation.
(h) to provide a device with a sealed abrasive reservoir that unseals in a single motion as the pressurized-gas delivery connector is attached to the device.
(i) to provide a device with means for regulating the gas-abrasive flow, so a single device is able to operate in a wide range of applications, from light etching to drilling and cutting.